The solubility of stibnite ( Sb(2)S(3)) was measured at 25 degrees C and 1 atmosphere in solutions ranging from 0.45 to 7.16 percent Na(2)S by weight. Sb(2)S(3): Na(2)S mole ratios of saturated solutions range from 0.238 to 0.403. Stibnite solubility increases at an increasing rate with rising Na(2)S concentration. The reaction that best fits the experimental data is 2Sb(2)S(3) + HS- + OH-= Sb(4)S(7)(2-) + H(2)O, for which an equilibrium constant was estimated to be about 5.0.